The invention relates to a process for preparing alkyl chlorosilanes which may have hydrogen in the presence of an alumina catalyst.
The preparation of alkylchlorosilanes by direct synthesis (Müller-Rochow synthesis) results, apart from the main dialkyldichlorosilane product, in further silanes such as tetraalkylsilane, trialkylchlorosilane, alkyltrichlorosilane inter alia, for which there is a varying demand and, in the event of an excess, a possible use is required. In the distillation of the crude silane mixture from the direct synthesis of alkylchlorosilanes and chlorosilanes, first runnings and intermediate fractions are also obtained, which cannot be utilized directly for further processing.
For instance, it is well known from the literature that aluminum chloride in all forms catalyzes the rearrangements, even on support materials such as aluminas. In US20030109735, the conversion in the trimethylsilane+methyltrichlorosilane or trimethylchlorosilane+methyltrichlorosilane reactions is improved by adding, for example, magnesium oxide to the aluminum chloride. DE 2351258 describes the addition of promoters to those reactions which minimize the discharge of aluminum chloride from the reaction vessel. EP 0971932, in contrast, describes the use of very pure alumina as a catalyst. The use of zeolites has also been described adequately, such as in EP 0146148.
It is an object of the invention to perform all conceivable rearrangement reactions in an apparatus with a very effective catalyst, not just with the pure substances, but also with mixtures of silanes with chlorine, hydrogen and alkyl radicals as substituents.